Understanding Chicken Egg Colour Genetics: Why Egg Colours Aren't as Simple as They Look
Walk into a backyard flock and you may find eggs in shades of white, cream, brown, chocolate, blue, green, olive, and everything in between.
But where do all of these colours come from?
Egg colour is one of the most fascinating aspects of chicken genetics—and it is something that has fascinated me personally since I began exploring breeding and egg colour more deeply.
Over the past couple of years, I have spent a great deal of time studying eggshell colour genetics, trying to better understand what is happening genetically to produce the incredible range of colours we see in chicken eggs.
The more I learn, the more fascinating I find it.
Because I have been learning so much through my own breeding projects, I wanted to take some of that information and share it here in a way that makes egg colour genetics easier for backyard chicken keepers and beginning breeders to understand.
I'm not a geneticist, and this isn't intended to be a genetics textbook. Rather, it is my attempt to take what I have been learning and explain the basic principles in practical, easy-to-understand terms.
And once you understand some of the basics, those beautiful blue, green, olive and brown eggs become even more interesting.
The Two Main Components of Egg Colour
To understand egg colour genetics, it helps to think about an eggshell as having two basic components:
The underlying shell colour
and
The pigments deposited onto the shell
The genetics controlling these components interact to create the final colour we see.
This is why two chickens can produce very different-looking eggs even though all eggshells are primarily made from calcium carbonate.
White and Brown Eggs: The Foundation
At the most basic level, chicken eggshells begin as a naturally pale shell.
Brown egg colour comes from pigments deposited onto the shell during the later stages of egg formation.
One of the primary brown pigments involved is protoporphyrin IX, along with other pigments that contribute to variations in brown shades.
The amount and combination of these pigments can influence whether an egg appears:
Cream
Light tan
Medium brown
Dark brown
Chocolate brown
This is one reason that "brown egg" isn't really one colour.
A Welsummer egg, for example, can look very different from the deep brown egg produced by a Copper Marans.
Even within the same breed or breeding line, individual hens can produce somewhat different shades.
What Makes an Egg Blue?
Blue eggs are different because of a genetic trait that causes the pigment biliverdin to be incorporated into the eggshell.
This results in a blue shell colour that can range from very pale blue to deeper blue shades.
The genetic factor associated with blue eggs is commonly referred to as the oocyan gene.
Breeds and breeding lines known for blue eggs include Araucanas, Ameraucanas, Cream Legbars, and Whiting True Blues.
However, even chickens carrying blue-egg genetics don't necessarily produce eggs that are all exactly the same shade.
There can be considerable variation.
So Where Do Green Eggs Come From?
This is where egg-colour genetics gets particularly interesting.
A green egg can essentially be thought of as a blue eggshell combined with brown pigment.
The blue component provides the underlying blue shell colour, while brown pigment deposited over that shell changes its appearance.
Depending on the genetics involved, the resulting egg can range from:
Blue → Blue-green → Green → Olive
The amount and intensity of brown pigment can influence how strongly the egg shifts toward green or olive.
This is one reason Olive Eggers have become so popular with backyard chicken keepers and breeders.
An Olive Egger isn't simply carrying a single "olive egg gene." Instead, breeders are combining genetics associated with blue eggshells and brown pigmentation.
Why Are Olive Eggs So Variable?
This is one of the most important things to understand when breeding for olive eggs.
Not all blue eggshell genetics are identical, and not all brown pigmentation is expressed at the same intensity.
As a result, breeding combinations can produce a range of egg colours rather than one predictable shade.
You might see offspring producing:
Pale green
Sage green
Medium green
Moss green
Olive
Dark olive
Sometimes the colour may be quite different from what you expected based solely on the parents.
This is because egg colour is influenced by multiple genetic factors, rather than being controlled by one simple "olive egg gene."
Brown Pigment Matters Too
When people think about breeding colourful eggs, they often focus heavily on the blue egg gene.
But the brown component is equally important when you're working toward green or olive eggs.
Consider two chickens that both carry blue-egg genetics.
If one also has genetics associated with stronger brown pigmentation, its offspring may have the potential to produce a very different green or olive egg than offspring from a bird with less brown pigmentation.
This is why breeders working toward darker olive or earthy-toned eggs often pay close attention to the brown-egg genetics in their breeding program, not just whether a bird carries blue.
Why Two Blue Egg Layers Don't Necessarily Produce the Same Blue
Even within a breeding group of blue egg layers, there can be variation.
One hen may produce a pale blue egg while another produces a stronger blue.
This is important for breeders because the colour of the egg laid by the mother is not necessarily a complete picture of all the genetics her offspring have inherited.
The offspring receives genetic material from both parents, and multiple genes can influence the resulting egg characteristics.
This is why breeders evaluate not only individual birds but also their breeding lines and the eggs produced by those lines over multiple generations.
Why Egg Colour Can Change During a Hen's Life
Genetics establishes the potential for egg colour, but genetics isn't the only factor that affects the egg we see.
A hen's egg colour can change during her laying cycle.
For example, a brown egg layer may produce darker eggs early in her laying cycle and gradually produce lighter eggs as the laying cycle continues.
Age and laying frequency can also influence the intensity of pigment deposited on the shell.
This is particularly noticeable with brown eggs.
So when evaluating a breeding bird, it is important not to base conclusions on one egg.
Looking at a hen's eggs over time gives you a much better understanding of her typical egg colour.
Why Breeding for Egg Colour Takes Time
This is where breeding becomes particularly interesting.
If you are simply crossing two chickens, you can often predict the general direction of the egg colour.
But developing a consistent breeding line is a different matter.
A breeder may be trying to combine:
Blue eggshell genetics
Strong brown pigmentation
Specific shades of brown
Egg colour intensity
Consistency from hen to hen
Those traits may not all appear together in the first generation.
Instead, breeders may need to evaluate offspring, select birds with desirable characteristics, and continue breeding over several generations.
This is why developing a breeding line is a process, rather than simply making one cross and expecting the desired result immediately.
Egg Colour Doesn't Tell You Everything About Genetics
This is another important point for anyone interested in breeding.
A chicken's egg colour gives you useful information, but it doesn't tell you every gene that bird carries.
Two hens may lay eggs that look very similar, but their offspring could produce noticeably different egg colours when bred to the same rooster.
Likewise, two eggs may look different even though the hens share some of the same underlying genetics.
This is why breeders keep records.
Egg colour observations, parentage, breeding combinations, and offspring results can all help build a better understanding of what is happening within a breeding line.
Different Breeding Combinations Can Produce Different Colour Palettes
One of the most fascinating parts of egg-colour genetics is that different combinations of genetics can produce very different colour ranges.
At Roslin Poultry Ranch, we work with several breeding lines that illustrate this variation.
Coastal Eggers: Blues, Light Greens & Spearmint
Our Coastal Egger line is developed around blue-egg genetics and is selected for a range of lighter, coastal-inspired shades.
Depending on the genetic combination, Coastal Eggers can produce eggs ranging from:
Blue
Blue-green
Light green
Spearmint
These colours demonstrate how different genetic combinations can produce a range of lighter shades rather than one standardized colour.
Available as: Hatching Eggs | Day-Old Chicks | Started Pullets
Rustic Eggers: Earthy Olives & Browns
Our Rustic Egger line takes a different direction.
These birds are part of our breeding work toward earthy-toned eggs, with shades ranging through:
Olive
Olive-brown
Brown
Deeper earthy tones
Rather than focusing on one specific shade, this line explores the natural range of olive and brown colours that can result from combining and selecting different egg-colour genetics.
Available as: Hatching Eggs | Day-Old Chicks | Started Pullets
Mosaic Eggers: Exploring a Developing Palette
Our newest breeding project is Mosaic Eggers.
This developing specialty breeding line brings together genetics from multiple breeding lines as we explore a range of:
Green
Olive
Brown
egg shades.
The name Mosaic reflects the idea behind the project: bringing different genetic pieces together to create a developing palette of egg colours.
Because egg colour involves multiple genetic factors, developing a breeding line like this is an ongoing process. Each generation provides an opportunity to evaluate the results and make new breeding selections.
Available as: Hatching Eggs | Day-Old Chicks | Started Pullets
Why Egg Colour Breeding Is So Interesting
One of the reasons egg-colour genetics is so fascinating is that the results aren't always perfectly predictable.
You can understand the genetics involved, make a carefully planned breeding cross, and still see variation among the offspring.
That's not necessarily a failure.
Variation is part of genetics.
For breeders, that variation provides an opportunity to select birds that move the breeding program closer to a particular goal.
Over time, careful selection can help develop lines that produce more consistent characteristics.
The Takeaway
Chicken egg colour is much more than simply "blue plus brown equals green."
The colour we see is influenced by the underlying eggshell colour, pigments deposited during shell formation, and multiple genetic factors that can vary from bird to bird.
That's why breeding for egg colour can be both challenging and fascinating.
A blue egg isn't necessarily just a blue egg.
A brown egg isn't necessarily just a brown egg.
And a green or olive egg can represent several different genetic components coming together.
For backyard chicken keepers, understanding these basics can make those colourful eggs even more interesting.
And for breeders, it opens the door to something much deeper: using genetics, careful selection, record keeping, and multiple generations to develop the egg colours you're working toward.
At Roslin Poultry Ranch, our Coastal Egger, Rustic Egger, and Mosaic Egger projects allow us to explore different parts of this fascinating spectrum of egg colour genetics—and we're excited to see where these breeding lines take us in the generations ahead.
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Great article!